SUBSPECIES STATUS:
The Willow Flycatcher was named by the American Ornithologist's Union in 1973
(AOU 1973) when the species E. traillii was divided into two species,
the Willow (E. traillii) and Alder (E. alnorum) Flycatchers. There
are five subspecies of the Willow Flycatcher currently recognized (Federal Register
1995, Browning 1993, Unitt 1987). Three of these subspecies occur in California
(Phillips 1948, Unitt 1987).

E.t. brewsteri
("Little Willow Flycatcher") Breeds
in California from Tulare County (S. Laymon, pers. comm.) north, along the western
side of the Sierra Nevada and Cascades, extending to the coast in northern California.

E.t. adastus:
Breeds in California east of the Sierra/Cascade axis, from the Oregon border
into Modoc County and possibly into northern Inyo County. (For the purposes
of this paper, populations at high elevation just east of the Sierra Nevada
crest but south of Modoc County are assumed to be E.t. brewsteri). There
has been very little study of E.t. adastus in California and therefore
this subspecies is not covered in depth in this report.

E.t. extimus
("Southwestern Willow Flycatcher") Breeds
in California from the Mexican border north to Independence in the Owens Valley,
the South Fork Kern River, and the Santa Ynez River in Santa Barbara County.

MANAGEMENT STATUS:
All three subspecies are listed as State Threatened and U.S. Forest Service
Region 5 Sensitive in California. The U.S. Fish and Wildlife Service has designated
the Willow Flycatcher a sensitive species in Region 1 (Washington, Oregon, Idaho,
California, and Nevada). E.t. extimus is federally listed as endangered
(Federal Register 1995).

E.t. brewsteri:
On the west side of the Sierra Nevada, Willow Flycatchers were considered
common summer residents in Yosemite Valley and surrounding areas (Grinnell and
Storer 1924, Gaines 1988), and in Sequoia and Kings Canyon National Parks and
surrounding areas (Sumner and Dixon 1953).

E.t. adastus:
One specimen of E.t. adastus, a Great Basin subspecies, is known
from Goose Lake, Modoc Co. (Harris 1997). Phillips (1948) thought that portions
of northern California might be a zone of intergradation between E.t. brewsteri
and E.t. adastus. The status of populations east of the Sierra/Cascade
crest between Goose Lake, Modoc County, and Independence, Inyo County, is unclear,
although they have been thought likely to be E.t. adastus (Unitt 1987).
On the east side of the Sierra Nevada, Willow Flycatchers were considered common
along the lower streams in the vicinity of Mono Lake (Grinnell and Storer 1924).

E.t. extimus:
This subspecies occurred in southern California, with its northern limits
represented by specimens from Independence (Inyo Co.), the South Fork Kern River
near Weldon (Kern Co.), and the San Fernando Valley (Los Angeles Co.) (Unitt
1987). Populations in southeastern California were probably restricted to the
Colorado River, but they were common there, e.g. 37 nests collected near Yuma
in 1902 (Unitt 1987). They were also common in swampy thickets around Los Angeles
(Belding 1890). It is probably this subspecies that Belding (1890) found a common
summer resident in the Central Valley, although there are no specimens from
the Central Valley in California museums. Other areas represented by museum
specimens include the Santa Ana River near Colton, San Bernardino County; San
Fernando Valley, Los Angeles County; and areas of Riverside County (Unitt 1987).
They were also observed along the Mohave River, San Bernardino County, and at
Santa Barbara, Santa Barbara County (Belding 1890). Willett (1912) considered
it a common summer resident in willow thickets of lowland southern California
occurring up to 1,520 m (5,000 ft) in mountain canyons. Other locations that
were probably occupied by the southwestern subspecies include: (1) Goldman's
(1908) account of Willow Flycatchers as "rather common in willow thickets and
tule marshes" from Summit Lake at the delta of the Kings and San Joaquin Rivers
south to Lake Buena Vista in Kern County; (2) Linton's (1908) referring to it
as a common breeder in the vicinity of Buena Vista Lake; and (3) Tyler's note
of encountering them "occasionally" in the willows along certain sloughs in
the Fresno district (Tyler 1916).

E.t. brewsteri:
In California, it is a rare to locally uncommon summer resident in wet meadows
and montane riparian habitats from 600 to 2,440 m (2,000-8,000 feet) in elevation
and a common spring (mid-May to early June) and fall (mid-August to early September)
migrant at lower elevations, primarily in riparian habitats, throughout the
state exclusive of the North coast (Zeiner et al. 1990). Most of the remaining
breeding populations occur in isolated mountain meadows of the Sierra Nevada
and Cascades (Serena 1982, Harris et al. 1988, B. Valentine pers. comm.). The
Perazzo Meadow/Little Truckee River/Lacey Valley area, in Sierra County, has
had a relatively stable population of breeding Willow Flycatchers known since
1982, with 23 to 36 singing males detected each year; there were 21 breeding
territories in the Perazzo and Little Truckee River areas in 1997 (Serena 1982,
Harris et al. 1988, Bombay 1998, S. Sanders, pers. comm.). A population of breeding
Willow Flycatchers was discovered at Red Lake, in Alpine County, in the early
1990s; there were five territories here in 1997 (Bombay 1998, R. Schlorff, pers.
comm.). A possible breeding population occurs along the Klamath River (S. Snaido,
pers. comm.).

Two newly discovered
populations documented in the Cascades during the past two years almost double
the known population of this subspecies in California. One population southeast
of McCloud, Siskiyou County, had 72 flycatchers in 1997 (C. Stermer, pers. comm.).
Another population in Warner Creek Valley, in northern Plumas County had 42
flycatchers in 1997 (S. Armentrout, pers. comm.).

E.t. adastus:
Willow Flycatchers were found breeding on the Owens River between Pleasant
Valley and Bishop in the summer of 1993 (Laymon and Williams 1994), and, based
on range, it is likely that these were E.t. adastus.

E.t. extimus:
Breeds from near sea level on the Santa Margarita River to 805 m (2640 ft.)
at the South Fork Kern River (Whitfield et al. 1997) and 914 m (3000 ft,) at
upper San Luis Rey River (Griffith Wildlife Biology 1995) in California and
to over 2,600 m (8530 ft.) in Arizona and southwestern Colorado (Sogge et al.
1997a). The largest remaining population in California is on the South Fork
Kern River, Kern Co. (Unitt 1987).

In southern California,
the Southwestern Willow Flycatcher breeds on the San Luis Rey River, San Diego
County; on Camp Pendleton, San Diego County on the Santa Margarita River and
Pilgrim, De Luz, French, and Las Flores creeks (Griffith Wildlife Biology 1995);
and on the Santa Ynez River, Santa Barbara County (Holmgren and Collins 1995;
US Fish and Wildlife Service 1997).

In 1996, breeding
was confirmed along the Arizona side of the lower Colorado River at Lake Mead
Delta (7 nests on 5 territories) and at Topock Marsh (1 nest) (McKernan 1997).
Other possible breeding sites on the lower Colorado River included North Lake
Havasu, Bill Williams River, Ehrenberg, Cibola Lake, Walker Lake, Ferguson Lake,
Mittry Lake, and Gila River (McKernan 1997).

The subspecies
E.t. extimus
has suffered severe declines throughout its range (Unitt 1987, U.S. Fish
and Wildlife Service 1993, 1995).

E.t. extimus:
Examination of museum specimens of 578 migrating and wintering Willow Flycatchers
located three definite and eight probable specimens of E.t. extimus indicating
that Guatemala to Costa Rica constitutes the main winter range (Unitt 1997).

ECOLOGY

AVERAGE TERRITORY
SIZE

Male Willow Flycatchers
establish territory boundaries prior to pair formation and maintain them early
in the season by singing from elevated perches. Territorial overlap between
adjacent males is minimal. Willow Flycatchers conduct most of their foraging
and other activities within their territories (KRCD 1985a), however both males
and females use adjacent areas (Sanders and Flett 1989). In southern Michigan,
1957-1964, average territory size was 0.7 ha (Walkinshaw 1966).

E.t. brewsteri:
Territory sizes for 6 paired males ranged from 0.09-0.38 ha and averaged
0.18 ha in eastern Fresno County, California (KRCD 1985b). On the Little Truckee
River in Sierra County, 22 territories ranged from 0.06-0.89 ha and averaged
0.34 ha (Sanders and Flett 1989). On the Little Truckee River, males and females
regularly used perches ranging from 4-30 m (13-98 ft) outside their defended
territory when feeding the young (Sanders and Flett 1989). Willow Flycatchers
may forage as far as 100 m (328 ft) from their territories at this time (Ibid).
Fledglings typically range into territories of adjacent pairs, often followed
by parents (KRCD 1985a). Little singing or chasing occurs at this time, indicating
a general decline of territory defense (Ettinger and King 1980).

Little is known
about each subspecies' pre-breeding season movements in California. Grinnell
and Miller (1944) reported that spring migration occurred in a wide distribution
over the lowlands of the State. At the South Fork Kern River from 1992 to 1997
(all subspecies), the average first arrival date was 27 April, the earliest
date was 16 April (1992), and the latest date of first spring arrival was 10
May (1997) (S. Laymon, pers. comm.). At desert oases in eastern Kern County,
Willow Flycatchers have been found from 7 May to 16 June with the peak migration
from mid-May to early June (M. Heindel pers. comm.). In the Sierra Nevada, the
earliest documented arrival date is May 15, 1926 (Gaines 1988). At Red Bluff,
Tehama County, spring migrants were rare (1976-1979); 13 individuals were recorded,
the earliest on 5 April, 1976, and the latest on 13 June, 1979 (Laymon 1981).
In a two year banding study on the Middle Rio Grande River in New Mexico, 42
spring migrants were captured from 13 May - 8 June, with the peak of migration
in the last week in May (Yong and Finch 1997).

Transients are
observed in the state through mid-September (Zeiner et al. 1990), but little
is known about each sub-species' post-breeding season movements in California.
Grinnell and Miller (1944) reported that post-breeding fall migrations may include
invasions of the species into habitat higher in elevation than the highest breeding
habitat. At desert oases in eastern Kern County, the earliest fall date is 28
July and the latest fall record is 18 October, with peak of migration from mid-August
to early September (M. Heindel, pers. comm.). At Coyote Creek Riparian Station,
Alviso, Santa Clara County (data for 1992, 1993, 1995), the earliest fall migration
date of 99 Willow Flycatchers captured was 9 August, 1992, and the latest was
9 October 1992, with the median capture date ranging from 29 August (1993) to
31 August (1992) (Bousman 1993, 1994, 1996). In the Sierra Nevada, the latest
fall record is 1 October (1926) (Gaines 1988). At Red Bluff, Tehama County,
fall migrants occurred from 7 August to 30 September, from 1976-1979 (Laymon
1981). In a two year banding study on the Middle Rio Grande River in New Mexico,
42 fall migrants were captured from August 9 to September 16, with no peak based
on weekly captures, and with adults showing a tendency to migrate earlier than
hatching-year birds (Yong and Finch 1997).

How to separate
migrating from breeding individuals. Willow Flycatchers (all subspecies) sing
during migration and E.t. brewsteri is one of the latest spring migrants
in North America (Unitt 1987). Thus, while E.t. extimus is already breeding,
E.t. brewsteri is still migrating through the region, and in southern
California may continue moving north until about 20 June (Garrett and Dunn 1981).
Thus, E.t. brewsteri may be present in the range of E.t. extimus
during much of the latter's breeding season, and single observations are often
useless in identifying breeding sites (Unitt 1987). Also, mated males may stop
singing during nesting. For this reason, sites must be surveyed a minimum of
three times. For E.t. extimus, Survey 1 should be conducted 15 - 31 May,
at which the earliest arriving males may have already established territories;
Survey 2 should be conducted 1 - 21 June when later arriving males will be singing
strongly and nesting activity may be detected (a male detected in Survey 1,
but not Survey 2 may have been a migrant); Survey 3 should be conducted 22 June
- 10 July, by which time all breeders will have arrived on their territories
and any singing males detected will be residents (Sogge et al. 1997a).

E.t. brewsteri:
In the Sierra Nevada, Willow Flycatchers arrive late in the breeding season
compared to other passerines nesting in Sierran meadows (Harris 1997, Sanders
and Flett 1989). Males arrive in late May to early June, and females arrive
about 1 week later (Garrett and Dunn 1981, Stafford and Valentine 1985). Weather
conditions on the breeding grounds can affect arrival date and subsequent nesting
activities (Stafford and Valentine 1985). In the central Sierra Nevada, the
heavy snowfall and long winter of 1983 delayed arrival by nearly a month relative
to 1984 (Stafford and Valentine 1985). Nest building in the central Sierra Nevada
usually begins within one week of pair formation (Stafford and Valentine 1985,
Harris 1997). Nest construction generally takes about eight days and the first
egg may be laid before the nest lining is complete.

In the central
Sierra Nevada, departure from breeding grounds usually occurs within a week
after the young have fledged. If a nest fails too late for the adults to attempt
a re-nest, the adults depart the breeding meadow. By mid-August of most years,
all Willow Flycatchers have departed (Valentine et al. 1988). Time of departure
from the breeding grounds was not synchronous; non-breeders left first followed
by breeders. Late departure dates reflect delayed on-set dates (Stafford and
Valentine 1985,Valentine et al. 1988).

E.t. extimus:
The southwestern subspecies arrives on the breeding grounds between early
May and early June (Sogge et al. 1997a). Successful breeders depart from breeding
territories as early as mid-August, and fledglings probably leave the breeding
area a week or two after adults, but few details are known (Sogge et al. 1997a).

MIGRATION STOPOVER
CHARACTERISTICS

While only a single
study was found on use of migratory stopover sites, it appears that Willow Flycatchers
stay only briefly at stopover sites. On the Middle Rio Grande River in New Mexico,
of 84 migrant Willow Flycatchers captured in two years, only seven were recaptured
(Yong and Finch 1997). All the recaptures occurred within one day of the initial
capture and had added on average 1.6% body mass/day. About 50% of the captures
had no fat stores, suggesting that stopovers are brief but frequent (Yong and
Finch 1997).

The range of
habitats used is much wider than that preferred for breeding and includes narrow,
linear riparian strips less than 10 m (33 ft) wide (Sogge et al. 1997a) and
shrubs and trees in parks and gardens (pers. obs.). On the Middle Rio Grande
River, netting was done in four habitat types: willow, cottonwood-Russian olive,
agricultural fields, and cottonwood-other habitats. Willow habitat had the highest
capture rate (n=34.1 birds/10,000 net hours), with dense young cottonwood-Russian
olive having the next highest rate (n= 16.0 birds/10,000 net hours) (Yong and
Finch 1997). Willow Flycatchers were observed flycatching and gleaning from
foliage. Vegetation structure probably also played a role, with more captures
occurring in habitats with dense shrub vegetation than in open, shrubless habitats
(i.e. cottonwood-other and agriculture).

FOOD HABITS

FORAGING STRATEGY

Willow Flycatchers
forage by either aerially gleaning (capturing an insect from a substrate while
hovering) from trees, shrubs, and herbaceous vegetation or hawking larger insects
by waiting on exposed forage perches and capturing insects in flight (Ettinger
and King 1980, Sanders and Flett 1989). Hawking appears to be more common than
aerial gleaning in mountain meadows and the opposite appears to be the case
in lowland riparian areas (Sanders and Flett 1989, J. Harris, pers. comm.).

DIET

A local, concentrated
source of nutrients in the form of flying insects is required to meet the nutritional
needs of territorial establishment and defense, mating, nest building, egg laying,
brooding, and nestling rearing. Bent (1942) states that 96% of the diet of this
species consists of animal matter, with most of this in the form of flying insects.
These insects are either attracted to water for consumptive proposes, or require
it for the aquatic phase of their life cycle. After the breeding season, when
Willow Flycatcher fledglings are able to forage for themselves and become more
mobile, the Willow Flycatchers are not as dependent on a localized food source.

In an examination
of stomach contents of 135 specimens, 96.05% of the diet was animal food and
3.95% of the diet was vegetable food (elderberry , blackberries, etc.) (Beal
1912 in Bent 1942). Hymenoptera (mostly wasps and bees) made up 41% of the diet,
Coleoptera were 18% of the diet, Diptera (such as crane, robber, house, and
dung flies) were 14%, Hemiptera were 8%, Lepidoptera (moths and caterpillars)
were 8%, and Orthoptera (mostly small grasshoppers) were 4%.

E.t. brewsteri:
In the area of Kings Canyon and Sequoia National Parks, the diet was reported
to be "wasps, bees, beetles, flies, caterpillars, moths, grasshoppers, and occasionally
berries" (Sumner and Dixon 1953).

E.t. extimus:
Food analysis using fecal samples from birds in Arizona and Colorado have
shown results similar to those reported in Bent (1942) with the addition that
Dragonflies (Odonata) composed 6% of the diet (K. Williams, pers. comm., citing
draft report by Drost et al.). Fecal samples from California have been collected,
but not yet analyzed (M. Sogge, pers. comm.).

"Given the extensive
geographic range of the Willow Flycatcher, it is not surprising that there is
geographic variation in the characteristics of Willow Flycatcher habitats. Even
in the western United States, substantial variation exists between the habitats
of Willow Flycatchers in Oregon and Washington as compared to the central and
southern Sierra Nevada or the southwestern region."

E.t. brewsteri
and E.t. adastus

"In Washington
and Oregon, several vegetation types have been mentioned in descriptions of
Willow Flycatcher habitat, including the following: deciduous growth around
the borders of clearings and brushy lowlands (Jewett et al. 1953); shrubby portions
of wooded stream bottoms (Gabrielson and Jewett 1940); willow thickets bordering
streamside lakes, woodland edges, young alder forests and tall brush at the
margins of fields (Gilligan et al. 1994); riparian hawthorne thickets, shrub
stratum of floodplain forest, upland prairie remnants with hawthorne, rose or
Prunus, and ninebark thickets at the lower edge of conifer forest (King
1955). Additional environmental features mentioned in these accounts include
openness of the shrub stratum (Jewett et al. 1953) and proximity to water (Gilligan
et al. 1994), although the immediate proximity of water is not an absolute requirement
(King 1955). A wide variety of deciduous plant species form the shrub stratum
in these vegetation types, including willow, alder, dogwood, hawthorne, rose,
elderberry, and Prunus spp. In Washington and Oregon, the Willow Flycatcher
appears to be a lowland species."

"In contrast,
habitat descriptions for the central and southern Sierra Nevada emphasize
riparian, willow-dominated vegetation (Grinnell and Miller 1944, Gaines
1988, Serena 1982, Harris et al. 1988) Habitat typically includes moist
meadows with perennial streams and smaller spring-fed or boggy areas with
willow (Salix spp.) or alder (Alnus spp.) (Serena 1982, Harris
et al. 1988). Willow Flycatchers have also been found in other riparian
environments of various types and sizes ranging from small willow-surrounded
lakes or ponds with a fringe of meadow or grassland to various willow-lined
streams, grasslands, or boggy areas. Breeding Willow Flycatchers have not
been detected above 2,500 m (8,000 feet) elevation in California."

"Non-shrub
trees do not appear to be a required habitat component, but Willow Flycatchers
will use scattered trees for singing and foraging perches and females will
use the foliage of trees as gleaning substrate during the nestling period
(KRCD 1985a, Harris et al. 1988, Sanders and Flett 1989). Several authors
describe edge, in the form of openings within thickets of riparian deciduous
shrubs, as an important component of Willow Flycatcher habitat (Walkinshaw
1966, Serena 1982, Harris et al. 1988, Sanders and Flett 1989)."

"The habitat descriptions
presented above suggest that Willow Flycatchers occupy a broader range of habitats
in Oregon and Washington than in the central and southern Sierra Nevada. The
range of shrub species utilized and the requirement for water are two aspects
of habitat that appear to change from north to south. Recent observations in
California (J. Villegas, pers. comm.) suggest that northern California Willow
Flycatchers might not conform to breeding habitat descriptions based on work
in the central and southern Sierra Nevada. In the Modoc National Forest, Willow
Flycatchers have been seen occupying breeding habitat with a shrub stratum of
Prunus, Ribes and other shrub species. Two nests have been found
in Cercocarpus. Surveyors should be aware that Willow Flycatchers may
occupy sites in the northern portions of California which more closely resemble
habitats described in Oregon and Washington than those described for the central
and southern Sierra Nevada. Surveyors should also be aware that migrating Willow
Flycatchers may occupy a wide range of environments that differ in shrub species
composition, slope and hydrology from those occupied during breeding activities."
(End of quotes from Harris 1997).

Valentine (1987)
suggested that an important character of Willow Flycatcher habitat in the central
Sierra Nevada was the openness of the tree canopy. He suggested that fire may
result in early successional stages that may provide usable nesting habitat.
This was based on a sighting of a territorial male that behaved as if paired
in a thick shrub field that was the result of an old forest fire. The site was
mesic and shrub species diversity was high, but the site was not a typical Sierra
Nevada Meadow (B. Valentine, pers. comm.).

E.t. extimus:
The Southwestern Willow Flycatcher is a riparian obligate species restricted
to dense stream-side vegetation. Four general habitat types are used by the
Southwestern Willow Flycatcher throughout its range: monotypic high-elevation
willow; monotypic exotic (dense stands of saltcedar [Tamarix] or Russian
olive [Elaeagnus]; native broadleaf dominated, and mixed native/exotic
(Sogge et al. 1997a). Of these, native broadleaf dominated and mixed native/exotic
are mainly used in California. The native broadleaf dominated habitat is composed
of a single species (e.g., Goodding's or other willow species) or a mixture
of broadleaf trees and shrubs, including cottonwood [Populus], willow
[Salix], box elder [Acer negundo], ash [Fraxinus], alder
[Alnus], and buttonbush [Cephalanthus], from 3 - 15 m (1 - 50
ft) tall, and characterized by trees of different size classes yielding multiple
layers of canopy (Sogge et al. 1997a). On the San Luis Rey River, the broadleaf
habitat is dominated by coast live oaks (Griffith Wildlife Biology 1995). The
mixed native/exotic habitat is composed of dense mixtures of native broadleaf
trees and shrubs mixed with introduced species such as salt cedar or Russian
olive. The vegetation of occupied sites includes dense patches often interspersed
with small openings, open water, or shorter vegetation, creating a mosaic that
is not uniformly dense (Sogge et al. 1997a).

NEST SITE

In general, willows,
alders, and cottonwoods or other riparian deciduous vegetation.

E.t. brewsteri:
In mountain meadows, Willow Flycatchers appear to prefer nesting near the
edges of vegetation clumps and near streams (Valentine et al. 1988, Sanders
and Flett 1989). In meadows along the little Truckee River, nests were built
in shrub willows (Salix lemmonii and S. jepsoni) (Sanders and
Flett 1989). Nests in these meadows are generally located in riparian deciduous
shrubs at least 2 m (6.6 feet) high, with a foliar density of approximately
50-70%, and with about 1 m (3.3 feet) of cover above the site (Harris et al.
1988, Sanders and Flett 1989). Nests are usually placed in a vertical fork of
a riparian deciduous shrub and built around supporting twigs (Stein 1963, Flett
and Sanders 1987, Valentine et al. 1988, Sanders and Flett 1989, Harris 1991).

E.t. adastus:
A vertical crotch or a horizontal or slanting fork with small branches that
can be woven into the nest are required (King 1955). Plants commonly used include
rose (Rosa), hawthorne (Crataegus), cow parsnip (Heracleum),
choke cherry (Prunus), and ninebark (Physocarpus) (King 1955).

On the South Fork
Kern River, Willow Flycatchers tend to nest in areas that have more trees greater
than 5 m (16 ft) tall, a larger amount of tree canopy cover, and a larger amount
of foliage volume from 0 to 4 m (0 to 13 ft) than random areas (Whitfield 1990).
Nests there occur typically in areas with multi-layered vegetation and fairly
high (60-65%) tree canopy cover (Whitfield and Enos 1996). In a study of 344
nests found during nine years of study on the South Fork Kern River, 244 (73%)
of nests were supported by willows, 46 (14%) were supported by a combination
of willow and nettle, 30 (9%) were supported entirely by nettle, 7 (2%) were
supported by mulefat, with the remaining nests occurring in cottonwood (Populus
fremontii), white alder (Alnus rhombifolia), and ash (Fraxinus
sp.) trees (Whitfield et al. 1997).

Along the lower
Colorado River in Arizona, seven nests were found in Goodding's black willow
(at Lake Mead Delta) and one in salt cedar (Tamarix sp.; at Topock Marsh;
McKernan 1997).

NEST SITE FIDELITY

In Michigan, Walkinshaw
(1966) found a return rate of 22.6% of females (n = 31) in the first year after
they were banded, 40.9% for males (n = 22) in the first year after they were
banded, and 1.4% for young (n=147). Only one female returned for a third year.
For males, 22.7% (n = 5) returned for a third year; 13.6% (n = 3) returned the
fourth year; and 4.5% (n = 1) returned the fifth year (Walkinshaw 1966).

E.t. brewsteri:
In the Sierra Nevada, return rates for adults have been 25% in the Little
Truckee River area (Sanders and Flett 1989) and about 31% for adults and nestlings
in the Shaver Lake area (5 of 12 banded adults and 4 banded nestlings; Stafford
and Valentine 1985). In the Little Truckee River area, of the four banded males
from 1986 that returned to breed in 1987, three returned to their 1986 territories
and one settled approximately 1 km (0.6 mi) from his 1986 site (Sanders and
Flett 1989). On Sierra National Forest, one pair returned to their same territory,
while one female on territory in 1983 nested successfully in 1984 at a site
approximately 14.5 km (9 mi) from her 1983 territory (Stafford and Valentine
1985).

E.t. extimus:
Site fidelity for birds banded as adults on the South Fork Kern River is
35.8%. Of 38 banded adult females, 34% were resighted in subsequent years, as
were 41% of 27 banded males (Whitfield and Enos 1996). Fledglings also show
a high return rate with 34% of 123 banded young returning the year after fledging,
and a few individuals returning for as many as five years (Whitfield and Enos
1996). Young fledging early in the season (before July 20th) are significantly
more likely to return in subsequent years than young fledged late in the season
(on July 20th or later), 22% vs. 6%, respectively (Whitfield and Strong 1995).

HEIGHT OF NEST

Typical nest
placement is such that the nests may be susceptible to damage from wind, cattle,
and predators (KRCD 1988, Valentine et al. 1988), although this susceptibility
may be more significant in the Sierra Nevada than in lowland riparian habitats
(Harris 1991).

E.t. brewsteri:
Nests in mountain meadows are generally located at about 1.1 to 2.5 m (3.6
to 8.2 feet) above the ground (Stein 1963, Flett and Sanders 1987, Valentine
et al. 1988, Sanders and Flett 1989, Harris 1991). Often, nests are about one
meter above the ground and about one meter below the top of the willow foliage
(Sanders and Flett 1989, Valentine et al. 1988). In the Tahoe, Toiyabe, and
Plumas National Forests in 1997, the mean height of 25 nests was 1.2 m (s =
0.3 m) from the ground (Bombay 1998).

E.t. extimus:
Nest height varies considerably, ranging from 0.6 to 18 m (2 to 59 ft) above
the ground (Sogge et al. 1997a). In an analysis based on 187 egg sets in museum
collections, nest height ranged from 0.6 m to 5.5 m (mean = 2.3 m, SD = 0.92
m; Unitt 1987). At
the South Fork Kern River, the average nest height is 2.2 m (SD = 1.36, n =
186) (Whitfield et al. 1997) Most nests (108 of 134) were between 0.6 and 3
m (2 - 10 ft) high, with the highest nest at 10 m (33 ft) (Whitfield et al.
1997). Nests were placed significantly higher and placed farther into willow
clumps at the Kern River Preserve (extimus subspecies) than those reported at
higher altitude study sites (KRCD 1988, Valentine et al. 1988). This may reflect
differences in habitat structure between the short, shrubby willows of montane
meadows and the larger willows characteristic of the lowland mature riparian
forest (Ibid). The later also provides large openings under the tree willow
canopy, allowing nest placement near an edge within the canopy but far from
the outer edge of the willow clump.

E.t. brewsteri:
Along the Little Truckee River, nest shrubs averaged 2.1 m tall (n = 20;
Sanders and Flett 1989). In the Tahoe, Toiyabe, and Plumas National Forests
in 1997, nests were an average of 0.9 m (3 ft) from the top of the shrub (n
= 25; Bombay 1998).

E.t. extimus:
On the South Fork Kern River, nesting areas are usually dominated by various
species of willows.

CANOPY COVER

Willow Flycatchers
generally do not occur in areas with dense tree cover although they will use
scattered trees on their territories for singing and foraging perches (Bent
1942, King 1955, Walkinshaw 1966).

E.t. extimus:
This subspecies seems to be an exception to the finding that Willow Flycatchers
do not occur in areas of dense tree cover. On the South Fork Kern River, mean
canopy cover on plots around the nest was 74.4%, range 22% - 100% (Whitfield
and Enos 1996). Although canopy cover can be dense, the flycatcher nests are
often in large openings under the willow canopy (Harris 1991).

AVERAGE TOP
CANOPY HEIGHT

E.t. brewsteri:
In the Sierra Nevada and Cascade mountains of California, Willow Flycatchers
nest in riparian deciduous shrub assemblages, usually willows, generally between
1 and 3 m (3.3 to 10 ft) in height (Serena 1982). Thus, average height of canopy
trees is not an important factor.

E.t. extimus:
On the South Fork Kern River, nesting sites are dominated by either Goodding's
black willow (Salix gooddingii) or red willow (S. laevigata).
On the upper San Luis Rey River the dominant canopy species is live oak (Quercus
agrifolia).

Several authors
describe openings as an important component of Willow Flycatcher habitat (Grinnell
and Storer 1924, Meanley 1952, King 1955, Walkinshaw 1966).

E.t. brewsteri:
Serena (1982) found that Willow Flycatchers in California had a preference
for tall clumps of shrubs separated by open areas. In the Little Truckee River
area, "willow flycatcher territories included willow clumps interspersed with
clearings. The willow cover on 22 territories ranged from 5% - 80% (mean = 44%,
SD = 22%)" (Sanders and Flett 1989). The willows ranged in height from 2 - 3
m. The critical factor was the availability of openings around the willow clumps;
no territories were located in areas with a solid contiguous mass of willows
(Sanders and Flett 1989).

E.t. adastus:
In a study in southeastern Washington, Willow Flycatchers occupied open,
park-like areas, avoided dense thickets, and were found on the edges of openings
and thickets (King 1955).

E.t. extimus
- No data

DOMINANT SHRUB
SPECIES

E.t. brewsteri:
In mountain meadows, willows are the dominant shrub.

E.t. extimus:
At the South Fork Kern River, mulefat (Baccharis salicifolia) is
the only shrub besides willows. On the upper San Luis Rey River, the dominant
shrub species are California Blackberry (Rubus ursinus), and California
Rose (Rosa californica) (Griffith Wildlife Biology 1995).

CO-DOMINANT
SHRUB SPECIES

E.t. brewsteri:
Azalea, dogwood (Cornus), and alder are present at many sites.

E.t. brewsteri:The ground
cover in Sierra Nevadan meadows occupied by Willow Flycatchers is dominated
by grasses, rushes, and sedges (Sanders and Flett 1989). In the Shaver Lake
area, vegetation density was relatively dense between 0.0 and 0.5 m (80% of
the points had cover) due to grasses, forbs, and willow stems (KRCD 1985b).
Duff from the previous season’s growth must be available for nest material.

E.t. extimus:
On the
South Fork Kern River, the average ground cover is 33.5% (SD = 27.25, n = 153),
with a range of 0% - 99% (Whitfield and Enos 1996). Ground cover is often sparse
in Willow Flycatcher territories because of the density of the canopy (mean
= 93.35%, S.D. = 1.04, range = 20% - 100%, n = 150), as well as the presence
of surface water (Whitfield and Enos 1996).

WATER

Nesting sites
in California are usually near languid streams, standing water, or seeps (Zeiner
et al. 1990). However, nests may be placed distant from water (e.g. where river
channels or subsurface flows have been modified), as long as the site continues
to support riparian vegetation (Sogge et al. 1997a). An example is a nest on
the South Fork Kern River that was 250 m (820 ft) from the nearest surface water
(Whitfield et al. 1997).

E.t. brewsteriIn California,
water is always present on Willow Flycatcher territories, in the form of running
water, standing water (pools), or saturated soils during the early stages of
the breeding season (Harris et al. 1988, Sanders and Flett 1989). Sites with
singing Willow Flycatchers were covered by a significantly higher percent of
water than sites where no flycatchers were detected (Harris et al. 1988).

E.t. extimusThe Southwestern
Willow Flycatcher breeds only near surface water or saturated soil, at least
during the early stages of pair formation and nest building (Sogge et al. 1997a;
Whitfield et al. 1997). Water may dry up and is not necessarily present at the
later stages of the breeding cycle.

LEAF LITTER

Little information
available.

E.t. extimus:Four of
14 nests studied on the upper San Luis Rey River were high in live oaks with
no tall shrubs or herbaceous vegetation under them, only leaf litter (Griffith
Wildlife Biology 1995). Leaf litter was not measured at nests on the South Fork
Kern, but the prevalence of flooding in the area would likely carry leaves away
(see discussion under bare ground).

BARE GROUND

E.t. extimus:
At the South Fork Kern River, Willow Flycatcher territories averaged 66.5%
bare ground or water and only 33.5% ground cover (Whitfield and Enos 1996).L. Slope: No information
available, but usually in flat or gently sloping areas.

DISTANCE TO
WATER

E.t. brewsteri:
Water is always present on Sierra Nevadan Willow Flycatcher territories,
in the form of running water, standing water (pools), or saturated soils (Harris
et al. 1988, Sanders and Flett 1989).

E.t. extimus:
Water is almost always present on Southwestern Willow Flycatcher territories,
at least at the beginning of the breeding season (Sogge et al. 1997a). At the
South Fork Kern River, distance from nest to nearest water averages 21.2 m (SD
= 4.4, range = 0-250 m, n = 140 nests; Whitfield et al. 1997). Almost half (46%)
of the nests were above water at the time they were built or shortly before
they were built (Whitfield et al. 1997).

NEST TYPE

An open-cup nest
is usually placed in a fork of a branch with several small diameter stems supporting
the nest. Nests are typically made of coarse and fine plant fibers, fine grasses,
and downy material from cattails, cottonwood and willow, and feathers (McCabe
1991). Fibers from dried milkweeds and nettles are commonly used (McCabe 1991,
M. Whitfield, pers. comm.). Often there is a loose streamer of material dangling
from the bottom (Sumner and Dixon 1953; Harrison 1975, Sanders and Flett 1989).

Adults frequently
dismantle a failed nest and move it to a new location (McCabe 1991), suggesting
that nesting material supply or the energetics of gathering nest material is
a limiting resource.

E.t. brewsteri:
Nests are made of grass and sedges. In mountain meadows, duff from the previous
growth season must be available when the flycatchers construct their nest (B.
Valentine, pers. comm.). Observations of the dismantling of old nests for the
construction of new nests were made by Stafford and Valentine (1985).

E.t. extimus:
Nests on the South Fork Kern River are often made of stinging nettle fiber
(M. Whitfield, pers. comm.), as well as thistle fibers, strands of dried willow
bark, grasses, animal hair, and the fluffy "cotton" borne by both willow and
cottonwood seeds (Harris 1991). Nests on the Colorado River in the Grand Canyon
are made of tamarisk leaves (Sogge et al. 1997b).

E.t. brewsteri:
In the Sierra Nevada, sally distances were usually less than 1 m (3.3 ft),
but occasionally were as far as 10 m (33 ft), from exposed perches (Sanders
and Flett 1989). Males hawked mostly from relatively high perches (greater than
3 m), while females foraged from perches in the lower willow branches, remaining
less conspicuous (Sanders and Flett 1989). Individuals were observed to shift
hawking perches every few minutes and sometimes use perches outside their territories
(Sanders and Flett 1989).

E.t. extimus:
At the South Fork Kern River, Southwestern Willow Flycatchers primarily
foraged in the middle third of the tree-like willows and tended to glean in
canopy spaces within the willows (J. Harris, pers. comm.).

BREEDING BIOLOGY

TYPICAL BREEDING
DENSITIES

E.t. brewsteri:
In the Sierra Nevada, densities at two study sites were 5 pairs per 40 ha
(100 acres) and 4 pairs per 40 ha (100 acres) (Sanders and Flett 1989). However,
because of the selection of specific microsites within meadows (e.g., wetter
areas), breeding density is difficult to calculate for this species. In the
Shaver Lake area at Long and Dinkey meadows, the density of Willow Flycatchers
in 1984 averaged 0.24 territories per ha or 9.6 pairs per 40 ha. (KRCD 1985b).
Single pairs of Willow Flycatchers are known to breed in the absence of other
individuals.

E.t. adastus:
In 1953, at the Palouse Hills in southeastern Washington, King (1955) observed
a density of 14 pairs breeding pairs per 40 ha (100 acres).

E.t. extimus:
At the Kern River Preserve, from 1994 to 1997, using all riparian habitat
in the study area, average breeding densities were 3 pairs per 40 ha (100 acres).
When using only the areas of habitat patches where nests were clustered, the
average breeding density was 15 pairs per 40 ha (Whitfield and Placer 1994,
Whitfield and Strong 1995, Whitfield and Enos 1996, Whitfield et al. 1997).
However, the location of breeding clusters is known to shift among years, and
not all sites are used each year (M. Whitfield, pers. Comm.).

INITIATION
OF NESTING

E.t. brewsteri:
On the Little Truckee River (Perazzo Meadow and Lacey Valley), in 1986 and
1987, the first eggs were laid in the third week in June and the first fledglings
appeared in mid-July (Sanders and Flett 1989). The last young fledged on 14
August in 1986 and the last fledgling was seen on 4 August in 1987 (Ibid). In
1997, of 25 nests monitored on the Tahoe, Toiyabe, and Plumas National Forests,
the first nests fledged around 21-22 July and the last fledged around 13-14
August (Bombay 1998). The latter nests were the result of renesting after the
first nests were lost to depredation (Ibid).

E.t. extimus:Nest
building usually begins within a week of pair formation. Egg laying can begin
as early as late May, but more often begins in mid-June. Chicks are present
in nests from mid-June through early August (Sogge et al. 1997a). On the South
Fork Kern River, the breeding season usually begins the last week in May extending
into late July, and rarely, into mid-August (Whitfield et al. 1997).

DISPLAYS

Males will use
the highest, most exposed perches, such as branches on the tops of willow shrubs
or on trees and snags, as singing perches. The distinctive male territorial
song is a "fitz-bew." Female Willow Flycatchers are also known to sing, and
will do so loudly and repeatedly (Seutin 1987, Sogge et al. 1997b). The songs
of females are identical to those of males (Seutin 1987), thus making estimation
of population size by monitoring singing birds much less certain, since each
singing bird may not represent a separate territory. Also, migrant individuals
may also sing, sometimes responding vigorously to tapes (Sogge et al. 1997b).

MATING SYSTEM

Generally monogamous,
although a few cases of polygyny have been reported (Prescott 1986; Sedgwick
and Knopf 1989; Sogge et al. 1997b and see below for references for California).

E.t. brewsteri:
A case of polygyny at Dinkey Meadow was reported in 1986 (Valentine et al.
1988) and one case was reported at Perazzo Meadows in 1993 (Powers 1993).

E.t. extimus:
Generally thought to be monogamous, but a high proportion of polygyny (10-40%)
observed at the South Fork Kern River (M. Whitfield, pers. comm.). In 1996,
four males were confirmed and three others were suspected to be polygynous (Whitfield
and Enos 1996), while in 1997, 13 of 35 to 37 males were polygynous, and only
seven females were mated monogamously (Whitfield et al. 1997).

CLUTCH SIZE

Full clutches
range from two to four eggs, with three to four being most typical (Bent 1942).
There is a record of a five egg clutch from southern Michigan (Walkinshaw 1966)
and from the South Fork Kern River (M. Whitfield, unpubl. data).

E.t. brewsteri:
Clutches of two to four eggs were found in the Little Truckee River area,
but of 18 full clutches, only one had two eggs (Sanders and Flett 1989).

E.t. extimus:
Full clutches ranged from two to four (n=44) in 1996 and 1997 on the South
Fork Kern River. One clutch had two eggs (2.3%), 23 clutches had three eggs
(52.3%), and 20 had four eggs (45.5%), for an average clutch size of 3.4 eggs
(Whitfield and Enos 1996; Whitfield et al. 1997). Based on dated clutches in
museum collections from coastal Southern California, 60% had four eggs and 40%
had three eggs (Unitt 1987). Clutches from the Colorado River were smaller;
18% had two eggs, 82% had three eggs, and none had four eggs (n = 28 unparasitized
clutches; Unitt 1987).

INCUBATION

Mainly females
(Ettinger and King 1980), but males have been recorded incubating in Arizona
(M. Whitfield, pers. comm.).

INCUBATION
PERIOD

Approximately
12 days after the last egg is laid (King 1955). Range of incubation periods
for eight nests in Michigan was 13-15 days (Walkinshaw 1966).E.t.
extimus: Incubation lasts 12 - 13 days from the date the last egg is laid,
and all eggs typically hatch within 24 - 48 hours of each other (Sogge et al.
1997a).

DEVELOPMENT
AT HATCHING

Young are altricial.
King (1955) gives a detailed description of growth and development and says
"the sequence of development does not differ markedly from that outlined by
Nice (1943) for open-nesting passerines in general."

NESTLING PERIOD

Nestling period
is 12 to 15 days (Sogge et al. 1997a, King 1955). Chicks can be present in the
nest from mid-June through early August, and young fledge typically from late
June through mid-August (Sogge et al. 1997a).

PARENTAL CARE

Nestlings are
brooded by the female only and are fed by both male and female, although the
female performs more than half the feedings (Ettinger and King 1980).

POST FLEDGING
BIOLOGY OF OFFSPRING

In Michigan, young
remained on their parent's territory for 10-11 days after fledging (Walkinshaw
1966).E.t.
extimus: Fledglings stay close to the nest and to each other for 3 - 5 days
after leaving the nest, and fledglings stay in the area for a minimum of 14
- 15 days (Sogge et al. 1997a).

DELAYED BREEDING

Little information
available, but probably breed as SY (second year) birds. On the South Fork Kern
many birds banded as nestlings have returned to breed in their first year as
adults (M. Whitfield, unpubl. data).

NUMBER OF BROODS

One brood, with
no renesting after a brood is reared, was recorded by Walkinshaw (1966) in Michigan
and by McCabe (1991) in Wisconsin.

E.t. brewsteri:
No pairs have been recorded as attempting another nest after successfully
rearing a brood (Stafford and Valentine 1985, Sanders and Flett 1987, Valentine
et al. 1988, Flett and Sanders 1989, Bombay 1998). Renesting attempts after
nest failures have been observed in the central Sierra Nevada (Stafford and
Valentine 1985). Two males that lost nests attempted renests, one with a new
female and the second with the same female. The brevity of the breeding season
in the Sierra Nevada probably limits the potential for renesting to only those
nests lost early in the breeding season.

E.t. extimus:
On the South Fork Kern River in the late 1980s, a probable case of double
brooding was documented when the first nest of the pair fledged only one young
(Whitfield 1990). In subsequent years of study on the Kern River, from 5 to
10% of successful pairs have been found to double brood (M. Whitfield, unpubl.
data). In Arizona and New Mexico there have been suspected cases of double brooding
(Sferra et al. 1997).

BROOD PARASITISM

Willow Flycatchers
are frequently parasitized by Brown-headed Cowbirds, especially in the lowland
portions of their range (Grinnell and Miller 1944, Friedman 1963). Friedmann
(1963) reported 150 instances of Brown-headed Cowbird parasitism of Willow Flycatchers;
41 of these were reports from southern California.

E.t. brewsteri:
Nesting failure due to cowbirds appears to be less in Sierra Nevadan montane
meadows than in lowland areas (Gaines 1977, Stafford and Valentine 1985, Valentine
et al. 1988, Sanders and Flett 1989). At least four instances of cowbird parasitism
are documented in the literature for the northern Sierra Nevada: Lake Tahoe
area (Gaines 1977), Lacey/Perazzo Meadow area (Sanders and Flett 1989), and
in Helen Bombay’s study to the north and south of Lake Tahoe (Bombay 1998).
In 1997, two of 25 nests were parasitized, then subsequently depredated (Bombay
1998). Cowbirds in montane Sierra Nevadan meadows nearly complete their breeding
season before Willow Flycatchers start nesting, which may explain this apparent
low rate of nest parasitism (Verner and Ritter 1983, Stafford and Valentine
1985).

E.t. extimus:
Intense parasitism was reported in 1987 on the Kern River Preserve, with
13 to 16 out of 19 nests parasitized by cowbirds (Harris 1991). At the South
Fork Kern River, an average of 63.5% of nests were parasitized from 1989 to
1992 with a range from 50% in 1989 to 80% in 1991 (Whitfield et al. 1997).

Cowbird trapping
has lowered the parasitism by Brown-headed Cowbirds to an average of 20.8% from
1993 to 1997 (range 38% in 1993 to 11% in 1996), stabilizing breeding populations
on the South Fork Kern River (Whitfield et al. 1997). Although cowbird trapping
has significantly increased Willow Flycatcher reproductive success at the South
Fork Kern, predation has been high enough to prevent an increase in the number
of breeding pairs thus far (Whitfield et al. 1997). Populations at Camp Pendleton
and the upper San Luis Rey River have increased due to cowbird trapping to protect
Least Bell's Vireos (Griffith Wildlife Biology 1995).

LANDSCAPE FACTORS

ELEVATION

Willow Flycatchers
are known to breed at elevations from near sea level to 2440 m (8,000 feet)
(Grinnell and Miller 1944, Zeiner et al. 1990). Historically the low elevations
of the San Joaquin and Sacramento valleys were probably the prime habitat.

FRAGMENTATION

Much of the riparian
deciduous shrub communities that historically provided habitat for Willow Flycatchers
have all but disappeared in California, especially in the Central Valley and
coastal southern California. Existing Willow Flycatcher habitat is widely dispersed,
mostly at small mountain meadows in the Sierra Nevada. In addition, for E.t.
brewsteri much of the remaining habitat in California exists at the geographic
and altitudinal extremes of the Willow Flycatcher’s range, where late spring
storms, isolation, or other unknown factors reduce the likelihood of successful
breeding.

Willow patch dynamics
in regard to Willow Flycatcher habitat suitability is still unknown. Various
authors describe openings as an important component of Willow Flycatcher nesting
habitat (Grinnell and Storer 1924, Meanley 1952, King 1955, Walkinshaw 1966).
In Sierra Nevadan montane meadows, willow thickets interspersed with open spaces
are typically used for nesting, while large, contiguous willow thickets are
avoided (Harris et al., 1988). Bombay (1998) found that 25 nests in the Tahoe,
Toiyabe, and Plumas National Forests were an average of 1.3 m (SD = 0.5 m) from
the closest shrub canopy opening. Sanders and Flett (1989) felt that openings
within willow patches appear to increase habitat suitability. However, in a
survey of 125 sites in the Sierra Nevada/Cascade mountain ranges, it was not
possible to predict presence or absence of Willow Flycatchers by willow clump
sizes (Harris et al. 1988). Nonetheless, some openness in the shrub stratum
seems important.

PATCH SIZE

E.t. brewsteri:
In California, the smallest area where E.t. brewsteri have been documented
nesting is the 0.25 ha Poison Meadow in the south central Sierra Nevada (KRCD
1985a). Fowler et al. (1991) felt that studies on the Little Truckee River and
surveys across California suggest this size is an absolute minimum. In two statewide
surveys, meadows 8 ha and larger made up the majority of the meadows in which
Willow Flycatchers were detected: in 1981, 20 out of 24 meadows with Willow
Flycatchers were greater than 8 ha in size (Serena 1982) and, in 1986, 104 out
of 111 singing male Willow Flycatchers were detected in meadows greater than
8 ha in size and none in meadows less than 4 ha in size (Harris et al. 1988).
In 1997, 25 nests in the Tahoe, Toiyabe, and Plumas National Forests were located
in patches that averaged 107 m2 (SD = 91 m2) in size (Bombay
1998).

E.t. extimus:
Southwestern Willow Flycatchers have nested in patches of riparian habitat
as small as 0.6 ha (e.g. Grand Canyon) (Sogge et al. 1995:14) and as large as
several hundred hectares (e.g. Roosevelt Lake and Lake Mead, Arizona) (Sogge
et al. 1997a). There are no records from narrow, linear riparian habitats less
than 10 m (33 ft) wide, although Willow Flycatchers will use such linear habitats
during migration (Sogge et al. 1997a). At the South Fork Kern River, the total
riparian forest is about 1,130 ha (2,800 acres), but the four major breeding
sites range from 7 to 24 ha (17 to 60 acres) in extent (S. Laymon, pers. comm.)

DISTURBANCE

Willow Flycatchers
in the Sierra Nevada have been observed nesting near trails created or maintained
by livestock. This placement near the edges of willow clumps makes the nests
susceptible to being knocked over by cattle (Stafford and Valentine 1985, Flett
and Sanders 1987, Valentine 1987, Valentine et al. 1988, Sanders and Flett 1989).

Livestock grazing
can also indirectly affect Willow Flycatcher habitat by altering the vegetation
and hydrology. Livestock can eat the lower branches of riparian deciduous shrubs
and consume or trample young riparian plants (Taylor 1986). A decrease in foliar
density within the lower 1.5 m (5 ft.) of riparian deciduous vegetation, where
most Willow Flycatcher nests occur, is of particular concern (Fowler et al.
1991). In Utah, Duff (1979) found that livestock exclusion resulted in an increase
in the portion of willow plants favored by Willow Flycatchers for nesting. In
Oregon, Taylor and Littlefield (1986) found that the increase in a Willow Flycatcher
population coincided with a dramatic decrease in the number of cattle using
the area and the elimination of willow cutting and spraying. In another area,
these authors found a negative statistical correlation between frequency of
cattle grazing on an annual basis and the numbers of Willow Flycatchers (Ibid).
Most of the studied areas had undergone prolonged (up to 50 years), intensive
annual grazing by livestock, as well as cutting and spraying of willows.

Heavy recreational
use of Willow Flycatcher habitat, especially uses such as off-road vehicles
that can compact soils, can negatively affect the quality of Willow Flycatcher
habitat and potentially cause direct disturbance to nesting birds.

ADJACENT LAND
USE

Land uses adjacent
to Willow Flycatcher habitat that can change the hydrology of the area can have
indirect negative effects on Willow Flycatcher habitat. Such uses include timber
harvest and associated ground-disturbing activities and ground water extraction.
Water impoundments can remove upstream Willow Flycatcher habitat and negatively
affect the hydrology of downstream habitat. Brown-headed cowbirds are associated
with pack stations and groups of livestock (Verner and Ritter 1983, Stafford
and Valentine 1985), and these land uses on lands adjacent to Willow Flycatcher
nests can cause an increase in the number of brown-headed cowbirds present to
potentially parasitize Willow Flycatcher nests. On the east side of the Sierra
Nevada, cowbirds can travel up to 6.7 km from feeding sites to parasitize the
nests of hosts (Rothstein et al. 1984).

PESTICIDE USE

No specific information
found. However, any activity that reduces insect abundance, particularly of
Hymenopterans and Dipterans, would negatively affect Willow Flycatchers.

The non-viability
of eggs was high in the Dinkey Meadow area (Valentine et al. 1988). Analysis
of the combined contents of three of the eggs by the Long Marine Laboratory
yielded 0.5 ppm of p,p'-DDE on a wet weight basis (B. Valentine, pers. comm.).
Because Willow Flycatchers spend almost 75% of their time outside the United
States where pesticide use is regulated differently, productivity of the nests
may be affected by out-of-country activities. The incidence of non-viability
needs to be followed to determine if the level noted by Valentine et al. (1988)
was an exception or a real issue.

PREDATORS

There is little
information on specific predators in the literature. Cases of documented predators
at nests include a milksnake (Lampropeltis triangulum) (McCabe 1991),
two common kingsnakes (Lampropeltis getulus) and a Cooper's Hawk (Accipiter
cooperii) (Paxton et al. 1997, McCarthey et al. 1997). A long-tailed weasel
(Mustela frenata) was seen in the vicinity of a newly depredated nest
in the Dinkey Meadow area (Stafford and Valentine 1985). There is evidence that
House Wrens may destroy eggs; Stafford and Valentine (1985) found an egg remaining
in a nest after the young had fledged that had two punctures in it, suggesting
the egg-pecking behavior of house wrens (Belles-Isles and Picman 1986).

E.t. extimus:
At the South Fork Kern River from 1989 to 1997, 36.3% of nests were lost
to predators, ranging from a low of 14% in 1992 to a high of 57% in 1997 (Whitfield
et al. 1997)

DEMOGRAPHY AND POPULATION
TRENDS

DEMOGRAPHICS

Survivorship

In Michigan, Walkinshaw
(1966) found a return rate of 22.6% of females (n = 31) in the first year after
they were banded, 40.9% for males (n = 22) in the first year after they were
banded, and 1.4% for young (n=147). Only one female returned for a third year.
For males, 22.7% (n = 5) returned for a third year; 13.6% (n = 3) returned the
fourth year; and 4.5% (n = 1) returned the fifth year (Walkinshaw 1966).

Reproductive
success

E.t. brewsteri:
In 1983 and 1984 on Dinkey and Long meadows, reproductive success for eight
nests is as follows: "Total of at least 24 eggs resulted in at least 18 nestlings
(75% egg to nestling success), of 18 nestlings 6 are known to have fledged (33%
nestling to fledgling success), another 3 probably fledged (raising to 50% success).
These equate to an egg to fledgling value between 25% and 38%. Over this period
three of the eight nests are likely to have fledged young (38%)" (KRCD 1985b).
In 1997 in the Tahoe, Toiyabe, and Plumas National Forests, 24 nests produced
75 eggs, with 28 confirmed fledglings (Bombay 1998).

There is complete
egg to fledging data for 5 of 11 nests at Perazzo Meadows and Lacey Valley in
1986; 14 eggs produced 5 fledglings (36%, Sanders and Flett 1989). For 1987
of 32 eggs (laid by 10 pairs) only six survived to fledging (19%, Ibid.). These
rates are significantly lower than the 46% egg to fledging rate for open-cup
nesters reported by Nice (1957).

The net reproductive
rate (the average number of female young produced by each female during her
lifetime) based on data from Sanders and Flett (1989) and KRCD (1985b) is 0.5,
indicating a declining population (Sanders and Flett 1989). (A rate of 1.0 indicates
a stable population).

E.t. extimus:
In 1994, on the upper San Luis Rey River, 7 of 11 nests of known fate succeeded
in fledging young (64% nest success), and 4 nests were taken by predators (Griffith
Wildlife Biology 1995). In 1996 and 1997, at the South Fork Kern River of 58
pairs observed, 24 pairs (41%) were successful on their first attempt and did
not initiate a second brood (calculated from data in Whitfield and Enos 1996,
Whitfield et al. 1997). Of the 34 pairs that failed, 27 (79%) renested, and
10 (37%) of these pairs were successful on their second try (Ibid.). Of those
17 pairs not successful on their second attempt, only 2 (11.8%) attempted a
third brood, but neither were successful (Ibid.). Therefore, of the 58 pairs
studied in 1996 and 1997, 34 pairs successfully fledged young for a 59% pair
success rate (Ibid.).

After Brown-headed
Cowbird trapping was initiated (years 1994-1997), the egg to fledgling ratio
on the South Fork Kern was 40% (168 fledglings from 420 eggs). The average number
of young fledged per female per year is 1.77 (low of 1.03 in 1997 and high of
2.54 in 1996); age at first breeding is one year; based on returns of banded
birds, 34.2% of females, 40.7% of males, and 34% of banded nestlings return
in at least one year to the study area; and the oldest bird detected to date
is a six year old male with 4 birds (3 females and 1 male) documented as five
years old (Whitfield and Placer 1994, Whitfield and Strong 1995, Whitfield and
Enos 1996, Whitfield et al. 1997, Whitfield unpubl. data).

POPULATION
TREND

There are insufficient
data to determine trends in California of any subspecies of Willow Flycatchers
or the species as a whole using Breeding Bird Survey (BBS) data (p = 0.24, n
= 14 routes between 1966 and 1996). Throughout North America, Willow Flycatchers
have shown a significant 1.2% per year decline from 1966 to 1996 (p = 0.01,
n = 1053 routes) (Sauer et al. 1997). During the same time period, the Western
BBS Region has experienced a 2.3% per year decline (p<0.01, n = 311 routes).
Oregon and Washington, where both E.t. brewsteri and E.t. adastus
occur, have both experienced significant declines of 5.8% per year (p = 0.01,
n = 61 routes) and 2.5% per year (p = 0.01, n = 57 routes), respectively from
1966 to 1996 (Sauer et al. 1997).

E.t. brewsteri:
A total of 121 singing males were located in the Sierra Nevada/Cascade mountains
of California in 1982 (Serena 1982), and 116 singing males were located statewide
in 1986 (Harris et al. 1988). In 1992, the California Department Fish and Game
estimated the state population, all subspecies, to be 200 pairs, with local
population sizes ranging from about 6 pairs to about 44 pairs (CDFG 1993). A
survey of 22 sites in the Sierra Nevada in 1995 detected 44 Willow Flycatchers
(26 singing males and 18 non-singing birds) (J. Harris, pers. comm.) The largest
population detected in 1995 was at the Little Truckee River (11 singing males,
8 non-singing) (J. Harris, pers. comm.) In 1997, a Sierra Nevadan-wide survey
of 145 sites detected 33 singing males at ten sites (M. Flores, pers. comm.).
Only three of the sites (Perazzo Meadow in Sierra County, Little Truckee in
Sierra County, and Red Lake in Alpine County) had more than one singing male
(Bombay 1998).

In the Sierra
Nevada, the species has declined (Harris 1987), becoming alarmingly scarce in
the Yosemite region (Gaines 1977, 1988). The consensus is that the population
in the Sierra Nevada has declined significantly during the past ten years, especially
populations on the west slope of the Sierra Nevada (Willow Flycatcher Working
Group meeting, January, 1998). However, the discovery of two new populations
in 1997 in the Cascades (see current breeding distribution) is encouraging.
The densities of willow flycatchers in 1997 at Perazzo Meadow and Lacey Valley
seemed about the same as those in 1986 and 1987 (Sanders 1998).

E.t. extimus:
In the last four decades, Willow Flycatchers have been eliminated from most
lower elevation habitats in the state (Unitt 1987). Recent declining population
trends are illustrated by declines from 1989 to 1992 at the South Fork Kern
River (Whitfield et al. 1997). However, cowbird control programs are credited
with stabilizing or increasing Willow Flycatcher populations at the South Fork
Kern River, Kern County, (Whitfield et al. 1997) and Camp Pendleton and the
upper San Luis Rey River, San Diego County (Griffith Wildlife Biology 1995).

MANAGEMENT ISSUES AND
OPTIONS

(1) Nest disturbance
by cattle. OPTIONS: (a) eliminate livestock use during the breeding season.
At the South Fork Kern River this would be from 15 May to 20 August (M. Whitfield,
pers. comm.); in the Shaver Lake area Valentine et al. (1988) suggest 1 July
to 20 August; in the central Sierra Nevada, Harris et al. (1988) suggest 1 June
to 15 August in areas where Willow Flycatchers breed. However, these dates will
not prevent damage to the understory, the preferred nesting sites, before the
Willow Flycatchers chose nest sites. (b) keep livestock from coming in physical
contact with nest sites during this period (e.g., by use of electric fences
where research is ongoing; Valentine et al. 1988).

(2) Livestock
grazing impacts on riparian deciduous vegetation. OPTIONS: (a) manage grazing
intensity or location to ensure riparian deciduous shrubs are not high-lined
(i.e., the foliar density in the lower portions of the shrubs is maintained)
and that recruitment of young riparian deciduous shrubs occurs.

(7) Brown-headed
cowbird nest parasitism. OPTIONS: (a) manage livestock so that aggregations
of livestock do not occur near Willow Flycatcher nest sites; (b) no new construction
of facilities such as pack stations, corrals, and salting facilities, which
concentrate livestock, within 3-6 miles of areas managed for nesting Willow
Flycatcher (Fowler et al. 1991, Verner and Ritter 1983). If these distances
are not attainable or if there are landscape features or habitat that concentrate
livestock, livestock use of aggregation areas should not occur during the breeding
season (USFS 1993); (c) implement a cowbird trapping program in selected areas
with both high Willow Flycatcher densities and high cowbird nest parasitism.

Although Willow
Flycatchers are relatively easy to detect, they are at such low numbers that
they can not be adequately monitored solely by multi-species monitoring techniques
(e.g., Breeding Bird Survey, Monitoring Avian Productivity and Survival sites).
A species-specific monitoring method should be used. An updated survey protocol
for E.t. extimus has been recently published (Sogge et al. 1997a, modifying
Tibbitts et al. 1994) and a protocol for National Forest Service lands in the
Pacific Southwest Region is in preparation. "Please note that federal endangered
species permits are required for surveys in all USFWS regions where the southwestern
willow flycatcher breeds" (Sogge et al. 1997a). The monitoring strategy
should include both wide-scale, periodic species-specific surveys and site-specific
monitoring of the demography at the primary population centers.

Research needs
include:

(1) Work to clarify
subspecies status in northern California and east of the Sierra Nevadan crest.
This should include work to identify subspecies genetically. For the purposes
of this paper Willow Flycatchers at high elevation on the east side of the Sierra
Nevada (Perazzo Meadow, Little Truckee River, and Red Lake) are assumed to be
E.t. brewsteri, because of their close proximity to other E.t. brewsteri
on the west slope, but this assumption must be tested. These sites support the
largest numbers of nesting Willow Flycatchers in the central Sierra Nevada.

(2) A statewide
survey for Willow Flycatchers, including all patches of suitable habitat
or potentially suitable breeding sites for all subspecies. Most surveys
conducted to date include only a portion of their range in the state. A
model from statewide surveys conducted in Arizona can be found in McCarthy
et al. 1998 and Sferra et al. 1997.

(3) Studies
of reproductive success, site fidelity, survivorship, and vegetation structure
of selected populations to determine net reproductive rate and contributing
factors. These studies will require banding of willow flycatchers. Identification
of environmental factors influencing these populations and identification
of source/sink areas can be determined from these data.

(4) Comparisons
of net reproductive rate and vegetation structure in grazed and ungrazed
areas. While curtailment of grazing in riparian zones with nesting Willow
Flycatchers from June through mid-August should occur on all sites to prevent
physical disturbance to Willow Flycatcher nests, some areas should be protected
year round from grazing to maintain high foliage density, eliminate browse
lines, and prevent soil compaction and gullying.

(5) Monitor
Willow Flycatcher population responses to meadow revegetation and restoration.
Monitoring should include other riparian meadow nesting species in addition
to Willow Flycatchers.

(6) Study
the importance of understory vegetation, particularly grasses and forbs,
to Willow Flycatcher nest success. In one year of study on the Tahoe and
Toiyabe National Forests, Bombay (1998) found lower nest success at a site
with cattle present during the nesting season versus ungrazed sites. This
lower success rate was not due to direct nest disturbance. The cause of
this lower success rate is unknown, but herbaceous vegetation around some
nest sites was reduced to less than two inches and it is known that Willow
Flycatchers commonly use fibers from dead standing plants to build their
nests.

(7) Study the
effects of human and livestock presence around Willow Flycatcher nests on the
behavior and nesting success of Willow Flycatchers. In the Tahoe and Toiyabe
National Forests, Bombay (1998) observed that "willow flycatchers are easily
agitated when humans are in the vicinity (10-20 m) of an active nest. When agitated,
they tend to become very vocal, and this in turn could attract nest predators."
This could have been a factor in the lower nest success rate observed in an
area with cattle present during the nesting season (see (5) above).

SCIENTIFIC
REFERENCES

AOU (American
Ornithologists' Union). 1973. Thirty-second Supplement to the American Ornithologists'
Union Checklist of North American Birds. Auk 90(2):411-419.

Powers, L. 1993.
Summary of monitoring efforts for a population of Willow Flycatchers in Perazzo
Meadows, 1992 and 1993. Work conducted by San Francisco State University’s Sierra
Nevada Field Campus in conjunction with USFS, Sierraville District, Tahoe National
Forest. Unpubl. Report 4pp.

U.S. Fish and
Wildlife Service. 1997. Biological and conference opinion on lower Colorado
River operations and maintenance - Lake Mead to southerly international boundary.
Albuquerque, New Mexico office.

Whitfield, M.J.,
and K. Enos. 1996. A Brown-headed Cowbird control program and monitoring for
the Southwestern Willow Flycatcher, South Fork Kern River, California, 1996.
Prepared for: U.S. Army Corps of Engineers, Sacramento District and the Calif.
Dept. of Fish and Game.